How to UV unwrap multiple animated objects at once
Follow these steps and you should be able to get this done.


Add a camera to the scene that points in the direction you want to project the texture. (Optionally, make it orthographic.)
Select all of the cubes you want to apply the texture to.
Run the simulation until you get to the frame where you want to apply the texture.
Add a UV project modifier to the active cube. Under the Projectors field, pick the projection camera you added from the list of objects.
In order to make sure that the image is being projected at the correct size, switch to Blender Render and the Textured view mode. In the N panel, set Shading to Multitexture and check Shadeless. This will let you preview the texture mapping independent of any material settings.
In the UV project modifier, pick the image you want to project from the list and check Override Image.
Press CtrlL to Make Links between the active and selected objects. You want to apply the UV project modifier to all the active objects so pick Modifiers from the list.
Make adjustments to the UV Project modifier in order to get the projection you want. You will need to re-link the modifier to the other objects after each change.
When you're happy with the results of the modifier use AltC, convert to Mesh in order to apply the UV Project modifier to all of the cubes.
Set up a material that uses the texture you're projecting and use CtrlL to link the materials to the other cubes.
Render out the image sequence and bob's your uncle.